Electronic digital logic circuitry – Function of and – or – nand – nor – or not
Reexamination Certificate
1999-09-13
2001-05-08
Tokar, Michael (Department: 2819)
Electronic digital logic circuitry
Function of and, or, nand, nor, or not
C326S016000, C714S724000
Reexamination Certificate
active
06229343
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of circuit technology. The invention concerns an integrated circuit including a functional device that can occupy a first and a second operating state, and a control device for switching between the states.
Clocked operating semiconductor memories, so-called SDPAMs, have a standby mode and an active mode, as described in Siemens Data Sheet “HYB39S64400/800/160AT(L), 64Mbit Synchronous DRAM”, Issue 7.98, Pages 7 to 13, in particular Page 8. The chip is in standby mode when the supply voltage is applied. The mode register is configured through input of a sequence of control signals and the active mode is set. The commands “Mode Register Set”, “Precharge All”, “Auto/Self Refresh”, and “Row Activate” must be input in that order. Including the supply voltage, eight terminal pins must be supplied with potential or signals: VDD, VSS, CKE, CS, CLK, RAS, CAS and WE.
During operation in the system, the signals are fed from a microcontroller over the chip housing terminals. In order to test functional features in the active mode during a semiconductor chip test, the test device must be capable of applying the above signals in the required sequence. Particularly, test equipment for visually inspecting a semiconductor slice at the end of manufacture and before being cut into the individual chips, often lacks appropriate devices for feeding such signals. Separately, eight needles must be set on the chip in order to feed in the signals. Chip area is hidden and visual inspection is restricted because semiconductor memory connection areas for input signals are not located near the edge of the chip but in its middle. As a result, manual positioning of the probe needles requires a considerable outlay of work and expense.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an integrated circuit having a two operating state functional device that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that can be tested in a simple way.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an integrated circuit, including: a functional device having a first mode of operation preset on start-up and a second mode of operation; a control device for receiving at least two control signals and for switching the functional device between the first mode of operation and the second mode of operation when a defined combination of the at least two control signals is received by the control device; a contact pad for receiving and transmitting a further control signal having a first state; and circuitry connected to the contact pad and to the control device, the circuitry generating and transmitting the defined combination of the at least two control signals to the control device in response to receiving the first state of the further control signal from the contact pad.
The circuitry for generating the control signal combination for the switchover between the operating states is connected such that the control signal is guaranteed to be inactive during normal operation if no control signal is applied to the test contact pad. A suitable way of doing this is to use a pull-up or pull-down resistor, depending on the polarity of an active control signal applied to the test contact pad. It is beneficial if the control signal at the test contact pad is low-active. Thus, a pull-up resistor is provided. In addition, it is also beneficial if a switching transistor that is controlled in opposition to the signal to be applied to the test contact pad is connected in parallel to the pull-up resistor. The signal injected at the test contact pad is combined through logic elements with the control signal combination that serves to switch between the operating states. The logic operation produces the effect that if an active control signal is applied to the test contact pad, that combination of signal states is generated through which a switchover takes place from standby mode into active mode. Otherwise, the logic elements are transparent for the control signals generated by the system controller.
In accordance with another feature of the invention, there is provided a resistor connected between the contact pad and a supply potential terminal, and another supply potential terminal connected to the circuitry, a voltage of the first state of the further control signal being equal to a supply voltage of the another supply potential terminal.
In accordance with a further feature of the invention, there is provided an inverter having an input and an output, and a switching transistor having a control input and a load path, the load path being connected in parallel to the resistor, the control input being connected to the output of the inverter and the input of the inverter being connected to the contact pad.
In accordance with an added feature of the invention, there is provided a second switching transistor having a second control input and a second load path, the second load path being connected in parallel to the resistor and the second control input being controlled by a signal that insures stable application of the integrated circuit supply voltage.
In accordance with an additional feature of the invention, the further control signal has at least one other state different from the first state and the circuitry includes a plurality of logic elements each having a first input connected to an input terminal for each one of the at least two control signals, a second input coupled to the contact pad and an output, wherein, in the first state of the further control signal, the defined combination of the at least two control signals is transmitted on the output to the control device, and, in the at least one other state of the further control signal, signals received at the first input of the logic elements are transmitted on the output to the control device.
In accordance with yet another feature of the invention, the at least two control signals are three control signals and there is provided two AND gates each having a first input, a second input and an output, an OR gate having a first input, a second input and an output and a second inverter having an input and an output, the input of the second inverter being connected to the output of the inverter, the output of the second inverter being connected with the first input of the two AND gates, the first control signal of the three control signals being input to the second input of a first of the two AND gates, the second control signal of the three control signals being input to the second input of a second of the two AND gates such that the output of the first of the two AND gates carries a first of the three control signals and the output of the second of the two AND gates carries a second of the three control signals and the input of the second inverter being connected with the first input of the OR gate, the third control signal of the three control signals being input to the second input of the OR gate such that the output of the OR gate carries the third control signal of the three control signals.
According to the invention, a single signal is transmitted through a contact pad to generate the combination of control signals that cause the switchover from one operating state to the other during normal operation. During testing of the integrated circuit it is necessary to feed only a single control signal and, in addition, the supply voltage. It is useful if the contact pad realized is considerably smaller than a conventional bonding pad provided for a bonding connection to a housing pin.
In accordance with a concomitant feature of the invention, there is provided at least one additional contact pad for connecting at least one of a group consisting of a supply potential and a signal, and the contact pad has an area between 10 and 1000 times smaller than an area of the at least one additional contact pad.
Other features that are considered as characteristic for the invent
Bauer Regine
Krause Gunnar
Cho James H.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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